|Publication number||US7602920 B2|
|Application number||US 10/049,025|
|Publication date||Oct 13, 2009|
|Filing date||Jun 8, 2001|
|Priority date||Jun 8, 2000|
|Also published as||CN1172477C, CN1386249A, EP1234284A1, US20020107798, WO2001095274A1, WO2001095274A8|
|Publication number||049025, 10049025, PCT/2001/1774, PCT/FR/1/001774, PCT/FR/1/01774, PCT/FR/2001/001774, PCT/FR/2001/01774, PCT/FR1/001774, PCT/FR1/01774, PCT/FR1001774, PCT/FR101774, PCT/FR2001/001774, PCT/FR2001/01774, PCT/FR2001001774, PCT/FR200101774, US 7602920 B2, US 7602920B2, US-B2-7602920, US7602920 B2, US7602920B2|
|Inventors||Patrice Hameau, Nicolas Fougeroux, Benoît Bole|
|Original Assignee||Cp8 Technologies|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (27), Referenced by (4), Classifications (33), Legal Events (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The subject matter of the subject invention is related to application Ser. No. 10/049,022 filed on Feb. 8, 2002, in the names of Patrice HAMEAU, Nicolas FOUGEROUX, and Benoit BOLE, entitled “METHOD FOR SECURE STORAGE OF SENSITIVE DATA IN A MEMORY OF AN EMBEDDED MICROCHIP SYSTEM, PARTICULARLY A SMART CARD, AND EMBEDDED SYSTEM IMPLEMENTING THE METHOD”, the subject matter of which is incorporated herein in its entirety.
1. Field of the Invention
The invention relates to a method for securing a predetermined operation, particularly the pre-initialization phase of an embedded microchip system, through the secure loading of a dedicated-use encryption key.
It applies more particularly to a smart card.
The invention also relates to an embedded system for implementing the method.
In the context of the invention, the term “pre-initialization” is meant in a general sense. It particularly relates to the manufacturing phase of a traditional smart card, or to the phase preceding the initialization phase of a so-called open smart card.
Likewise, the term “embedded system” refers to various systems or devices having in common the fact of using a microchip comprising data storage and data processing means, generally constituted by a microprocessor or a microcontroller. Such an embedded system can be constituted, in particular, by a smart card.
To illustrate the concept, we will consider hereinafter the preferred application of the invention, i.e., the pre-initialization of a smart card.
2. Description of the Related Art
In most smart card-based applications, various functions related to security are devolved to the smart cards. This term itself covers various concepts: confidentiality, authentication, etc.
For this reason, written into a nonvolatile part of the aforementioned storage means of the microchip, in permanent (using “Read Only Memory” or “ROM”), or semi-permanent (“Electrically Erasable Programmable Read Only Memory” or “EEPROM”) fashion, is so-called secret data required for these functions: encryption algorithm, secret encryption keys, identification data, etc.
Among this data, there is a so-called fabrication key that traditionally makes it possible to secure all of the steps for pre-initializing the smart card.
Normally, the manufacture of a smart card takes place in two main phases. During the first phase, a microchip is manufactured by a first entity, which will hereinafter be called the “chip manufacturer.” During a second phase, this microchip is packaged, then integrated into a substrate, i.e. an approximately rectangular piece of plastic, which constitutes the smart card per se. This operation is generally performed by a second entity, different from the first, which will hereinafter be called the “card manufacturer.”
A third entity, which will hereinafter be called a “pre-personalizer,” performs the aforementioned pre-initialization operation.
In the prior art, almost systematically, the fabrication key that secures all of the steps in the pre-initialization of a smart card is written in unencrypted form, and without prior authentication by the card manufacturer. This operating mode poses several problems:
One solution would be to have the fabrication key written by the chip manufacturer during a so-called probe operation, but this solution is very costly, since the secret data must be changed for each card (non-static data), which moreover is detrimental to the production rate of the chip manufacturer. This costly method is therefore not realistic, and because of this, is practically never implemented.
The object of the invention is to eliminate the drawbacks of the devices of the prior art, some of which have just been mentioned.
To this end, according to a first advantageous characteristic of the invention, the writing of the fabrication key is protected by a mutual authentication between an element known as a “SAM” (for “Security Access Module”) and the smart card, in order to prevail over the utilization of a phony “SAM” module in which a cloned smart card or even one having a falsified ROM or other nonvolatile memory. Hereinafter, for simplification purposes, this module will be called “SAM.” It can be hosted in a microcomputer or a smart card, for example. Generally, the “SAM” can be defined as being a “key holding” element. In essence, it stores a secret key that is never divulged, in the sense that it is not communicated to the outside world. It is used to calculate other keys that allow the aforementioned mutual identification.
The authentication of the “SAM” by the smart card uses an asymmetric encryption algorithm. It can be, for example, the algorithm widely used in the field of banking applications and known by the abbreviation “RSA” (for “Rivest, Shamir and Adleman,” the designated inventors in U.S. Pat. No. 4,405,829 A). However, since a smart card is only equipped with limited computing resources, it is preferable to use the so-called “Rabin” algorithm for this purpose. In fact, in the latter case, less computing power required, which is more suitable for the specific characteristics of a smart card or similar type of device. Also, hereinafter, without in any way limiting the scope of the invention, the asymmetric algorithm used will be considered to be the “Rabin” algorithm.
As for the authentication of the smart card by the “SAM” module, it is advantageously based on a symmetric algorithm, preferably of the so-called “Triple DES” (“Data Encryption System”) type.
By using the Rabin algorithm for the authentication of the “SAM” by the smart card and the “Triple DES” algorithm for the authentication of the smart card by the “SAM,” the use of a cryptoprocessor is not necessary in order to implement the security mechanism, which is also advantageous in the context of the applications envisaged by the invention.
The method according to the invention then allows the authenticated “SAM” to load the fabrication key securely into the smart card, which is itself authenticated.
Hence, the main subject of the invention is a method for secure loading of a key dedicated to securing a predetermined operation into storage means of a microchip of an embedded system, said dedicated key being contained in a security device that includes means for two-way communication with said microchip, characterized in that, said storage means of said microchip storing a symmetric secret encryption key and an asymmetric public key and said security device storing the same symmetric secret encryption key and the asymmetric secret key corresponding to the public key of said microchip, it comprises:
Another subject of the invention is an embedded microchip system for implementing the method.
The invention will now be described in greater detail by referring to the attached drawings, in which:
Hereinafter, without in any way limiting its scope, we will concentrate on the context of the preferred application of the invention, unless otherwise indicated, i.e., the securing of the pre-initialization phase of a smart card.
The method according to the invention, from the point of view of the smart card and the “SAM” module, requires a symmetric secret key that will hereinafter be called the master key KM. This key KM must be present when the microchip, or “chip,” leaves the entity that is called the “chip manufacturer.”
The storage of this key KM takes place in a nonvolatile part of the memory with which the microchip is equipped: a permanent memory of the ROM type, or semipermanent memory of the EEPROM or a similar type.
In a preferred variant of embodiment of the invention, and according to a first characteristic, the key KM is “probe” written into EEPROM by the chip manufacturer. The bytes that compose the key KM are extremely sensitive data and must be treated as security bytes. Storage in EEPROM allows this key KM to be diversified for several batches of cards.
The method according to the invention, from the smart card point of view, also requires an asymmetric public key that will hereinafter be called the asymmetric public key n. This k, set for all the cards, must be present when the microchip or chip leaves the entity called the “chip manufacturer.”
The storage of this key n takes place in a nonvolatile part of the memory with which the microchip is equipped: a permanent memory of the ROM type and/or semi-permanent memory of the EEPROM or a similar type.
In a preferred variant of embodiment of the invention, and according to a second characteristic, the nonvolatile memory of the microchip has a particular hybrid—physical and logical—configuration. A permanent part of the ROM type and a re-programmable, semi-permanent part of the EEPROM type are provided. The bytes of the aforementioned public key are distributed between these two storage areas in the particular way explained below. The bytes must be present when the chip leaves the chip manufacturer.
The “probe” written bytes in the EEPROM part of the memory must be considered to be extremely sensitive, and in this respect, must be treated as security bytes.
For example, to illustrate the concept, we will consider a public key with a length of 768 bits (or 96 bytes). The latter resides completely in ROM. However, according to a preferred embodiment of the method according to the invention, one byte per block of twelve is intentionally stored in an erroneous way in the ROM type storage area, this erroneous value having been purposely written into the code stored in this ROM type part of the memory. The correct value of the byte in question is stored in the EEPROM type part. In this example, eight bytes (i.e., 96/12=8) must therefore be programmed into the EEPROM type part of the memory. This data is static, since a public key is not diversified.
In addition, an operation known as a “hash” is performed on 160 bits of the public key n. The result is stored in ROM, so that it can be verified with each utilization of the key n. To do this, an algorithm of the type known as “SHA-1” is advantageously used. This particular algorithm must therefore be installed in the smart card.
Associated with the particular storage of the public key n, the hash makes it possible to simultaneously guarantee the integrity of both the ROM and EEPROM type parts of the memory.
We will now describe the steps for the secure loading of a so-called fabrication key into the smart card.
The first phase of the method according to the invention consists in the authentication of the “SAM” vis-à-vis the smart card CP.
This phase specifically includes a step for the calculation by the “SAM” of a cryptogram, using an asymmetric secret key corresponding to the asymmetric public key n contained in the card. In practice, the key is composed of two first numbers, which will arbitrarily be called p and q. The asymmetric secret key of the “SAM” will arbitrarily be called Kpq. In other words, the “SAM” is identified vis-à-vis the smart card CP and the latter recognizes its caller with the public key n.
As shown in
A Rabin signature, which will hereinafter be named SR, is calculated by the “SAM” 3 on ninety-six bytes of data, referenced DSR. This data DSR can conform to the concatenation illustrated by
The five-byte header string of the mutual authentication command, DSR2, can advantageously be constituted by the contents of a command of the type known as an “APDU” if the smart card CP is read by a smart card reader using a protocol in accordance with the standards ISO 7816-1 through ISO 7816-4. More precisely, it can be the code associated with a loading instruction.
Referring again to
The second phase of the method consists in the authentication of the smart card CP vis-à-vis the “SAM” 3, so as to complete the mutual authentication of the two entities.
From the secret master key KM and from the aforementioned sixteen-byte random number NaC, the smart card CP generates a sixteen-byte symmetric, secret so-called session key KS, making it possible to calculate a cryptogram specific to the smart card CP.
Preferably, this secret session key KS, called an authentication key, is obtained by performing in encryption using an algorithm of the Triple DES type on both parts, NaC1, and NaC2, of the card random number NaC.
More precisely, the process for calculating the secret session key KS is executed as illustrated by the diagram of
As is well known, an encryption with an algorithm of the Triple DES type includes, in cascade, a first encryption using a key (in this case the secret master key KM) via a direct DES, a second DES of the inverse type, and a third DES, also direct.
In the eight-byte “low-order” part NaC1 of the smart card random number NaC, the Triple DES is performed directly using three cascaded modules, referenced D11, D21 and D31. The modules D11 and D31 receive, through their key inputs, the same key value, in this case the eight-byte “high-order” part KM1 of the key KM, while the module D21 receives in its key input the “low-order” part KM2, also eight bytes. On output from the module D31, the eight-byte “high-order” part KS1 of the secret session key KS is obtained. This eight-byte word KS1 can be temporarily stored in a storage register or in a part of the RAM with which the smart card CP is normally equipped.
The part KS1 is re-injected through a first input of a logic circuit of the “exclusive-OR” type, referenced XOR. The latter receives, in a second input, the eight-byte “high-order” part NaC2 of the smart card random number NaC. The output of the logic circuit XOR is transmitted to the input of a Triple DES encryption chain. This Triple DES is performed using three cascading modules. referenced D12, D22 and D32. As above, the modules D12 and D32 receive, through their key inputs, the same key value, in this case the eight-byte “high-order” part KM1 of the key KM, while the module D22 receives in its key input the “low-order” part KM2, also eight bytes. On output from the module D32, the eight-byte “low-order” part KS2 of the secret session key KS is obtained. This eight-byte word KS2 can also be temporarily stored in a storage register or in a part of the RAM.
The secret key KM can be present in ROM, or “probe” written in EEPROM, as mentioned above.
It is clear that the “exclusive-OR” logic operation can be performed by means of software instead of using a specific logic circuit XOR, by calling a routine stored in “ROM” memory 1, for example, under the control of the microprocessor CPU. Likewise, the “DES” and “DES−1” operations are generally performed by means of algorithms stored in “ROM” memory 1, again under the command of the microprocessor CPU. The intermediate results are stored in registers or in RAM.
The “SAM” 3 is capable of calculating the same secret session key KS in the manner just described, since the latter also stores the secret master key KM.
In an additional step, the smart card CP generates a byte string that will hereinafter be called the “card cryptogram” CC. The latter is obtained by encrypting the “SAM” random number transmitted to the smart card CP using the secret session key KS that has just been calculated.
The “SAM” random number NaS has been received from the “SAM” 3 and is temporarily stored in a register or other storage location. The eight-byte high-order part NaS1 of this random number NaS is subjected to a Triple DES by the chain D11 à D31. However, it is first subjected to an “exclusive-OR” logic operation with an initial chaining value of eight bytes Nf, of hexadecimal value “00,” by means of a first circuit XOR1 (or by a software process). It is the output from this circuit XOR1 that is transmitted to the aforementioned chain. The encryption key is the secret session key KS calculated in the preceding step. More precisely, the key inputs of the “DESs” D11 et D31, receive the eight highest-order bytes KS1 of this key KS, and the key input of the DES D21 receives the eight lowest-order bytes KS2.
This process makes it possible to calculate the eight highest-order bytes CC1 of the cryptogram CC. These bytes CC1 are re-injected as input into the Triple DES encryption chain D12 à D32 for the lowest-order bytes NaS2 of the “SAM” random number NaS, more exactly into one of the inputs of a second “exclusive-OR” circuit XOR2, the first input receiving the eight lowest-order bytes of the random number NaS. It is the output from this circuit XOR2 that is transmitted to the aforementioned chain. The key inputs of the “DESs” D12 et D32 receive the eight highest-order bytes KS, of this key KS, and the key input of the DES D22 receives the eight lowest-order bytes KS2. The output of the DES D32 generates the eight low-order bytes CC2 of the card cryptogram CC.
This cryptogram is transmitted to the “SAM” 3 by means of the input-output order OES (
The last step consists of loading said fabrication key KF into the memory of the smart card CP, using a loading command Cch. This key KF is protected by encryption by means of the secret session key KS, in a mode known as “CBC” (for “Cipher Block Chaining”).
If the loading command fails, the session key KS is lost and a new mutual authentication is necessary, with a calculation of a new session key.
The loading command is signed by means of a Rabin signature by the “SAM” 3.
In all, DSR′ comprises ninety-six bytes. In the example, DSR′ comprises three parts:
Through the reading of the above, it is easy to see that the invention achieves the stated objects.
In particular, the loading of the fabrication key subsequently used to secure the steps for pre-initializing the smart card CP takes place with a very high level of security. The method makes it possible to load, into each smart card CP, its own key, or in other words a different key than the other smart cards.
However, although it allows this key diversification, the method does not make it necessary to resort to long and costly operations of the type indicated, known as “probe writing by the chip manufacturer.”
It should be clear, however, that the invention is not limited to just the exemplary embodiments explicitly described, particularly in connection with
As indicated above, although the Rabin algorithm is particularly advantageous, as it consumes few computing resources, this algorithm could be replaced by other types of asymmetric algorithms, such as “RSA.” The same goes for the algorithm of the Triple DES type. Other symmetric key algorithms can be used without going beyond the scope of the invention. This is merely a technological choice that is within the capability of one skilled in the art, and depends particularly on the precise application envisaged.
Likewise, the precise numerical values, the number of bytes or other elements, are indicated only to illustrate the concepts and do not in any way limit the scope of the invention. In particular, as is well known, the length of the encryption keys depends on the degree of security one expects to achieve, and can result from technological choices, for example linked to the standards in force and/or to the types of algorithms chosen.
Lastly, as indicated, the invention is not limited to smart card-based applications only. It can be applied in the context of any embedded system comprising a microchip or similar device, into which it is necessary to load a key for securing predetermined operations.
The operations in question can be pre-initialization operations, as described in detail, but also other types of operations.
For example, it is possible to subject sensitive commands from a so-called open smart card, such as the loading of libraries of the type known as “APIs” (“Application Program Interface”) or various codes, into the EEPROM part, to a mutual authentication between the loading device and the smart card, the mutual authentication process being executed according to the method of the invention.
In general, it is possible, from the smart card point of view, to assign a public key and a symmetric secret key to each type of operation to be secured. The session key derived during the authentication mechanism can subsequently be used to secure the loading of another key for a dedicated use, such as protecting libraries of the aforementioned “API” type or “patches,” i.e. the application of binary data to replace all or part of an existing program.
While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth herein, are intended to be illustrative, not limiting. Various changes may be made without departing from the true spirit and full scope of the invention as set forth herein and defined in the claims.
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|U.S. Classification||380/278, 726/34, 726/26, 726/2, 705/41, 713/194, 726/9, 380/229, 713/1, 713/173, 380/249, 726/27, 713/169, 713/172|
|International Classification||H04L9/32, G06K19/10, G06K17/00, H04L9/08, H04L9/00, H04L9/10, G06K19/07, G07F7/10|
|Cooperative Classification||H04L9/0844, H04L9/0625, H04L9/0897, H04L9/3249, H04L9/3273, G06Q20/341, G06Q20/40975, G06Q20/105, G07F7/0826, G07F7/1008, G06Q20/3558|
|Feb 8, 2002||AS||Assignment|
Owner name: BULL CP8, FRANCE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HAMEAU, PATRICE;FOUGEROUX, NICOLAS;BOLE, BENOIT;REEL/FRAME:012809/0602
Effective date: 20000620
|Feb 24, 2004||AS||Assignment|
Owner name: CP8 TECHNOLOGIES, FRANCE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BULL CP8;REEL/FRAME:014981/0001
Effective date: 20001230
|Jan 5, 2010||CC||Certificate of correction|
|Oct 5, 2010||CC||Certificate of correction|
|May 24, 2013||REMI||Maintenance fee reminder mailed|
|Oct 13, 2013||LAPS||Lapse for failure to pay maintenance fees|
|Dec 3, 2013||FP||Expired due to failure to pay maintenance fee|
Effective date: 20131013